Resin composition and sliding member

ABSTRACT

A sliding member includes: a base material; a coating layer formed on the base material and made of a resin composition including: a binder resin including polyamideimide; PTFE dispersed in the binder resin; and at least one of graphite and MoS 2  dispersed in the binder resin; wherein a surface roughness of the coating layer after a sliding test is equal to or less than the surface roughness of the coating layer before the sliding test.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of InternationalApplication No. PCT/JP2017/041337, filed on Nov. 16, 2017, which claimspriority to Japanese Application No. 2016-224317, filed on Nov. 17,2016. The entire disclosures of the above applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a sliding member.

RELATED ART

To improve characteristics of a sliding surface, a sliding material witha resin coating layer is known, in which PTFE, graphite, and MoS₂ areused as additives in a binder resin (refer to JP 2002-310345 and JP2008-056750).

In the technology disclosed in JP 2002-310345 and JP 2008-056750, aproblem exists in that a solid lubricant is liable to fall off or cleaveunder a high-load state, as a result of which the sliding surfacebecomes rougher. When the sliding surface becomes rough, formation of anoil film is impeded, particularly where an amount of oil present is low,or in a dry environment where a supply of lubricating oil isinsufficient. Under such circumstances, abrasion and seizure resistancedecreases.

The present invention provides a technique for improving wear andseizure resistance under a high load state in an environment where asupply of lubricating oil supply is insufficient.

SUMMARY

The present invention provides a sliding member including: a basematerial; a coating layer formed on the base material and made of aresin composition including the following a binder resin includingpolyamideimide; PTFE dispersed in the binder resin; and at least one ofgraphite and MoS2 dispersed in the binder resin; wherein a surfaceroughness of the coating layer after a sliding test is equal to or lessthan the surface roughness of the coating layer before the sliding test,the sliding test being carried out under the following condition:

Testing device: Oil spray type poor lubrication tester

Speed: 6.3 m/sec

Surface pressure: 2 to 20 MPa (incremental increase: 2 MPa/min.)

Time: up to 10 min.

Lubrication method: Spray

Lubricating oil: refrigeration oil

Counterpart material: Bearing steel.

The surface roughness after the sliding test may be equal to or lessthan the half of the surface roughness before the sliding test.

The surface roughness after the sliding test may be equal to or lessthan 2.1 μm RzJIS.

Advantageous Effect

According to the present invention, wear and seizure resistance can beimproved under a high load state in an environment where a supply oflubricating oil is insufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing the structure ofcompressor 1 according to one embodiment.

FIG. 2 illustrates an example of the positional relationship betweenswash plate 3 and shoes 5.

FIG. 3 illustrates an exemplary cross-sectional structure of swash plate3.

FIG. 4 shows a surface pressure measured in a contact resistance test.

FIGS. 5A-5C show states of sliding surfaces before and after slidingtests.

DETAILED DESCRIPTION 1. Configuration

FIG. 1 is a schematic cross-sectional view showing the structure ofcompressor 1 according to one embodiment of the present invention.Compressor 1 is a swash plate type compressor. Compressor 1 includesshaft 2, swash plate 3, piston 4 and shoe 5. Shaft 2 is rotatablysupported relative to a housing (not shown in the figures). Swash plate3 is fixed at an oblique angle relative to the axis of rotation of shaft2. Swash plate 3 is an example of the sliding member according to thepresent invention. Piston 4 reciprocates in a cylinder bore (not shownin the figures) provided in the housing. Shoe 5 is provided betweenswash plate 3 and piston 4 and slides with each of swash plate 3 andpiston 4, respectively. In shoe 5, the surface that slides with swashplate 3 is substantially flat, and the surface sliding with piston 4 hasa dome-like (hemispherical) shape. Shoe 5 is an example of a matingmember that slides on the sliding member according to the presentinvention. The rotation of shaft 2 is converted to the reciprocatingmotion of piston 4 by swash plate 3.

FIG. 2 illustrates an example of the positional relationship betweenswash plate 3 and shoes 5. FIG. 2 is a view from a directionperpendicular to the sliding surface. Swash plate 3 is disk-shapedoverall, and has a hole at its center. Viewed from swash plate 3, shoe 5performs rotational movement on the sliding surface. Here, “rotationalmovement” refers to a movement by which shoe 5 defines a circulartrajectory relative to swash plate 3.

FIG. 3 illustrates an exemplary cross-sectional structure of swash plate3. FIG. 3 is a schematic view showing a structure in cross sectionperpendicular to the surface that slides with shoe 5. Swash plate 3 hasa substrate 31, coating layer 32, and coating layer 33. Coating layer 32and coating layer 33 both slide on shoe 5. Each of coating layer 32 andcoating layer 33 are examples of the coating layer according to thepresent invention. The base material 31 is formed to be disk-shaped witha hole at its center. The base material is made of an alloy satisfyingthe required characteristics, for example, the material is aniron-based, copper-based, or aluminum-based alloy. From the viewpoint ofpreventing adhesion with shoe 5, swash plate 3 is preferably made of amaterial different from that of shoe 5.

Coating layer 32 is formed to improve the characteristics of the slidingsurface of swash plate 3. Coating layer 32 is made of a resincomposition. The resin composition includes a binder resin and anadditive dispersed in the binder resin. The binder resin is made of, forexample, a thermosetting resin. At least one of polyamideimide (PAI),polyamide (PA), and polyimide (PI), epoxy, and phenol is used as thethermosetting resin, for example. Among these, the binder resinpreferably includes at least one of PAI and PI. For example, the contentof the binder resin in the resin composition is preferably 50 to 80 vol%. More preferably, the content of the binder resin is more than 60 vol%. More preferably, the upper limit of the content of the binder resinis 75 vol %.

A solid lubricant is used as the additive. The solid lubricant is addedto improve lubricating properties, in other words, to reduce acoefficient of friction. For example, the resin composition includes 20to 50 vol % of solid lubricant in total. PTFE (polytetrafluoroethylene)is used as the solid lubricant. Furthermore, this resin compositionincludes, in addition to PTFE, at least one of graphite (Gr) and MoS₂.The content of MoS₂ is preferably less than the content of PTFE. Forexample, the content of PTFE is 10 to 30 vol %, and more preferably 15to 25 vol %. The content of MoS₂ is 0 to 10 vol %, preferably 0 to 4 vol% (that is, MoS₂ may not be included). The content of graphite ispreferably 0 to 20 vol %, more preferably 10 to 20 vol %. Moreover, itis preferable that the content of MoS₂ is less than the content ofgraphite.

The average particle diameter of the additive added to the binder resinis preferably less than 10 μm, and more preferably, equal to or lessthan 5 μm, in order to enhance the smoothness of the sliding surface andto assist the formation of an oil film. Here, the average particlediameter means the 50% diameter (median diameter) in the distribution ofthe sphere equivalent diameter obtained by the laser diffraction methodin the state of the raw material before mixing with the binder resin.When the average particle diameter of the additive is less than 10 μm,the sliding surface is maintained smooth, in contrast to where theaverage particle diameter of the additive is equal to or less than 10μm, and as a result formation of an oil film is enhanced. Therefore,transition from boundary lubrication to mixed lubrication or fluidlubrication is facilitated, and enhanced lubrication is easily obtainedeven under severe conditions such as low oil content and high load.

The average particle size of PTFE is preferably larger than either theaverage particle size of graphite or the average particle size of MoS₂.The inventors of the present invention hypothesize that by using PTFEhaving an average particle diameter larger than that of graphite andMoS₂, the PTFE is stretched on the sliding surface to cover the graphiteor MoS₂, whereby smoothness of the sliding surface is easily maintained.

The resin composition may further include hard particles as theadditive. As the hard particle, at least one of an oxide, a nitride, acarbide, and a sulfide is used, for example. The average particle sizeof the hard particles is preferably less than 10 μm, and more preferablysmaller than the average particle size of PTFE.

Coating layer 33 is also formed using the same resin composition ascoating layer 32. In the substrate 31, the surface that acts as thesliding surface, that is, the surface on which coating layer 32 isformed and the surface on which coating layer 33 is formed aresubstantially flat. The surface of the substrate 31 may be roughened toenhance the adhesion to coating layer 32. In addition, an intermediatelayer may be formed between the substrate 31 and coating layer 32.

The present invention is not limited to the above embodiment and variousmodifications can be applied to the embodiment. For example, the slidingmember having a coating layer formed using the resin compositionaccording to the present embodiment is not limited to a swash plate fora compressor. The sliding member may be a shoe for a compressor, or ahalf bearing, a bush, or a thrust washer used in an engine.

2. Experiment Examples

The present inventors manufactured test pieces of the sliding memberunder various conditions. The present inventors evaluated theircharacteristics. Cast iron was used as the base material of the slidingmember. The base material was processed to have the shape of the swashplate shown in FIG. 1. The coating layer was formed on this basematerial, and was made of the resin composition described in Table 1.PAI was used as the binder resin. Experiment Example 3 is an examplewhere the average particle size of MoS₂ is larger than the averageparticle size of PTFE.

TABLE 1 PTFE Gr. MoS₂ binder average average average resin particleparticle particle vol vol size vol size vol size % % (μm) % (μm) % (μm)Experiment Val. 16 5 18 2 2 2 Example 1 Experiment Val. 20 5 18 2 not —Example 2 included Experiment Val. 11 5 16 2 19  20  Example 3

First, the abrasion resistance test was performed on the test pieces ofthe above three experiment examples. The test conditions of the abrasionresistance test were as follows.

Test equipment: High pressure atmosphere friction and wear tester

Speed: 40 m/sec

Surface pressure: 4 to 12 MPa (increased incrementally by 2 MPa/3 min)

Time: Hold for 1 hour at maximum surface pressure

Atmosphere: refrigerant and poor lubrication

Counterpart material: Bearing steel

The present inventor observed the sliding surface of the test piecesafter the test, and confirmed whether the coating layer was worn or not.Although abrasion occurred in Experiment Example 3, no abrasion wasfound in Experiment Examples 1 and 2. Thus, compared with ExperimentExample 3, Experiment Examples 1 and 2 showed improved wear resistance.

Furthermore, the present inventors performed a seizure resistance teston the test pieces of Experiment Examples 1 and 2. The test conditionsof the seizure resistance test were as follows.

Testing device: Oil spray type poor lubrication tester

Speed: 6.3 m/sec

Surface pressure: 2 to 20 MPa (incremental increase: 2 MPa/min.)

Time: up to 10 min.

Lubrication method: Spray

Lubricating oil: refrigeration oil

Counterpart material: Bearing steel

FIG. 4 shows the surface pressure measured in the contact resistancetest. While seizure occurred in the test piece of Experiment Example 3at a surface pressure of 10 MPa, no seizure occurred in the test piecesof Experiment Examples 1 and 2 even at a maximum surface pressure of 20MPa of the test apparatus. Thus, compared with Experiment Example 3,Experiment Examples 1 and 2 showed improved seizure resistance.

Furthermore, the present inventors performed a sliding test on the testpieces of Experiment Examples 1 and 2, and measured the surfaceroughness of the sliding surface before and after the test using asurface roughness meter (SP81B manufactured by Kosaka Laboratory).Further, the surface was observed with an electron microscope. The testconditions of the sliding test were the same as those of the seizureresistance test described above.

FIGS. 5A-5C show states of sliding surfaces before and after slidingtests. FIG. 5A shows Experiment Example 1, FIG. 5B shows ExperimentExample 2, and FIG. 5C shows Experiment Example 3. It is of note thatthe surface roughness is measured according to the ten-point averageroughness RzJIS defined in JIS B 0601: 2001. While the surface roughnessincreased in Experiment Example 3 during the sliding test, the surfaceroughness decreased in Experiment Examples 1 and 2 during the slidingtest. The surface roughness after the sliding test was equal to or lessthan the half of the surface roughness before the sliding test. Further,the surface roughness after the sliding test was equal to or less than2.1 μm RzJIS. In other words, while the surface became rougher inExperiment Example 3 after use, the surface became smoother inExperiment Examples 1 and 2 after use.

The invention claimed is:
 1. A sliding member comprising: a basematerial; and a coating layer formed on the base material and made of aresin composition including: greater than or equal to about 50 vol. % toless than or equal to about 80 vol. % of a binder resin includingpolyamideimide; greater than or equal to about 10 vol % to less than orequal to about 30 vol. % of PTFE dispersed in the binder resin; greaterthan or equal to 10 vol. % to less than or equal to 20 vol. % ofgraphite dispersed in the binder resin; and greater than 0 vol. % toless than or equal to about 10 vol. % of MoS₂ dispersed in the binderresin, wherein the coating layer is free of a PTFE film forming agent,wherein each of the PTFE, graphite, and MoS₂ has an average particlediameter less than 5 micrometers, and wherein a surface roughness of thecoating layer after a sliding test is equal to or less than the surfaceroughness of the coating layer before the sliding test, the sliding testbeing carried out under the following condition: Testing device: Oilspray type poor lubrication tester Speed: 6.3 m/sec Surface pressure: 2to 20 MPa (incremental increase: 2 MPa/min.) Time: up to 10 min.Lubrication method: Spray Lubricating oil: refrigeration oil Counterpartmaterial: Bearing steel.
 2. The sliding member according to claim 1,wherein the surface roughness after the sliding test is equal to or lessthan the half of the surface roughness before the sliding test.
 3. Thesliding member according to claim 1, wherein the surface roughness afterthe sliding test is equal to or less than 2.1 μm.
 4. The sliding memberaccording to claim 2, wherein the surface roughness after the slidingtest is equal to or less than 2.1 μm.
 5. The sliding member according toclaim 1, wherein the average particle diameter of the PTFE is greaterthan that of the graphite, and the average particle diameter of the PTFEis greater than that of the MoS₂.